1. Field
The disclosed embodiments relate to a system for the spraying of spray liquid for aircraft windshields. More specifically, the disclosed embodiments relate to a purging device used to clean a spray system of this kind and eliminate all traces of spray liquid from the piping system after the spraying of such liquid. The disclosed embodiments also relate to an aircraft cockpit comprising at least one such system for the spraying of spray liquid.
When an aircraft is in flight, and in the event of heavy rain, there are known ways of improving visibility inside the aircraft cockpit by spraying a hydrophobic liquid or water-repellent liquid, most usually consisting of silicone or solvent, on the exterior of the windshield of said cockpit. The water-repellent liquid is preferably used when the aircraft is in flight because, when the aircraft is on the ground, this water-repellent liquid cannot be sprayed fast enough on the windshield.
2. Description of the Prior Art
There are known prior-art spraying systems integrated into aircraft and enabling the spraying, on command, of the water-repellent liquid on the windshield of the cockpit.
FIG. 1, pertaining to the prior art, gives a schematic view of a water-repellent spraying system 1 of this kind for aircraft windshields.
The water-repellent liquid spraying system 1 is provided with a water-repellent liquid supply circuit 2 comprising a piping system 3 designed to convey the water-repellent liquid from a tank 4, at a distance from the windshield 6, up to two nozzles 5 situated at the level of the windshield 6 of the aircraft cockpit. The water-repellent liquid is projected to the nozzles 5 through pressure within the tank 4. Generally, when said tank is full, the pressure in said tank 4 is at five bars. When the tank is empty, the pressure falls to two bars.
The aircraft pilot and/or co-pilot exercise remote control over the opening of the valves 7, situated upstream from the nozzles 5, so as to let the water-repellent liquid flow up to the nozzles 5. The term “upstream” refers to that which comes before the point considered, in the sense of flow of liquid in the supply circuit 2. When the valves 7 are closed, they block the pressurized water-repellent liquid within the piping system 3. In the event of heavy rain, to improve visibility through the windshield 6, the pilot and/or co-pilot press the control button 8 situated in the cockpit, thus actuating the temporary opening of the valves 7. When water-repellent liquid no longer needs to be sprayed on the windshield 6, the pilot and/or copilot releases the control button 8, thus closing the valves 7. The flow of water-repellent liquid is once again blocked upstream relative to the nozzles 5, at the valves 7.
The water-repellent liquid used to improve visibility through the windshield 6 has the main drawback of gradually clogging the piping system by the accumulated depositing of silicone on the walls of the piping system and in the nozzles 5. There is therefore a known way of draining the portion 9 of the supply circuit 2 situated downstream from the valves 7 so as to clean the piping system and the nozzles 5 once the water-repellent liquid has been sprayed on the windshield 6.
In the prior art, as shown in FIG. 1, the purging device 10 has a tubing 11 constantly conveying pressurized air tapped at the aircraft engines, provided that the engines are working, from a collector 12 to the nozzles 5, passing through the portion 9 of the piping system 3 situated downstream from the valves 7. Thus, the assembly formed by said portion 9 and the nozzles 5 is purged of any residue of water-repellent liquid that may get deposited once the valves 7 are closed. Furthermore, and in order to prevent any water-repellent liquid that may be contained in the downstream portion 9 of the piping system 3 of the supply circuit 2 from flowing inside the tube 11 of the purging device 10, it is possible to provide said purging device 10 with backflow check valves 13 positioned at the connection between the tube 11 of the purging device 10 and the piping system 3 of the water-repellent liquid supply circuit 2. The backflow check valves 13 permit the passage of compressed air toward the nozzles 5 and prevent the water-repellent liquid from flowing in the reverse direction.
In order that the water-repellent liquid may be sprayed before the pressurized gas when visibility through the windshield 6 has to be improved, there are known ways of maintaining the pressure of compressed air in the tube 11, at the inlet of the backflow check valves 13, at a pressure that is approximately equal to 60 millibars and in any case strictly below the pressure of the water-repellent liquid. In general, the pressure of the water-repellent liquid ranges from 5 bars to 2 bars since there is little loss of pressure during the journey in the piping system 3 of the supply circuit 2. One of the drawbacks of the prior-art purging device 10 is that it necessitates the use of a tubing 11 that transits from the nose of the aircraft to the central section of said aircraft in which the turbo-jet engines are situated. The tube 11 has a length approximately equal to 30 meters and is subjected to numerous constraints since the pressurized gas flows therein constantly.
Furthermore, the installation of the purging device 10 is a lengthy, complex process. For, it is necessary to define the tube 11 with the constraints of segregation of the systems, use fixed supports spaced out at intervals of 0.5 meters approximately and hence pierce the structure of the aircraft in order to fix these supports. The piercing in itself requires validation design studies to ensure that it does not inappropriately weaken the structure of the aircraft. Furthermore, it is necessary to match the definitions of the tubing portions from one aircraft section to another, manufacture, bend, equip and protect the entire tube 11, install the tubing portions on each of the aircraft sections etc. The test procedure can be performed only when the entire purging device 10 is connected together on the final assembly line. The test therefore can only be done once the aircraft has been assembled and the purging device 10 has been positioned, thus making it necessary to have specific tools for the pressurizing of the pneumatic circuit.
The phases of the definition, manufacture, installation and testing of the prior-art purging device 10 thus entail a major loss of time.